I. Introduction
This invention relates to positive-working photoresist compositions. More particularly, this invention relates to photoresist compositions containing a light sensitive component that is the condensation product of an o-quinone diazide sulfonyl compound and a vinyl ether. The photoresists of the invention are characterized by increased photospeed and enhanced inhibition.
II. Description of the Prior Art
Photoresist compositions are well known in the art and described in numerous publications including DeForest, Photoresist Materials and Processes, McGraw-Hill Book Company, New York, 1975. Photoresist coating compositions are applied from liquid solution or as a dry film. When coated onto a substrate and exposed to light of the proper wavelength, are chemically altered in their solubility to certain solvents (developers). Two types are known. The negative-acting resist is initially a mixture which is soluble in its developer, but following exposure to activating radiation, becomes insoluble in developer thereby defining a latent image. Positive-acting resists work in the opposite fashion, light exposure making the resist soluble in developer.
The photoactive compound used in many positive acting photoresists is an o-quinone diazide sulfonic acid ester of a relatively large molecular weight polyhydroxy phenol. This material is costly relative to the other components of the photoresist. However, photoresists using such photoactive compounds can be developed to yield relief images having linewidths of one micron or less. In addition, considering the cross-section of a photoresist image, the channels formed in the resist by development have square corners and sidewalls with only minimal taper.
The positive-working photoresists typically comprise a light-sensitive component in a film-forming, alkali soluble, thermoplastic polymer binder. The light-sensitive compounds or photoactive compounds most frequently used are esters formed by reacting an o-quinone diazide sulfonyl acid halides with a light insensitive phenol (PACs). The phenol is used to increase the size of the total molecule to thereby prevent loss by sublimation, migration of the PAC within a photoresist coating, and to increase inhibition of the resist. Recently, the industry has moved to use of PACs that are condensation products of several moles of an o-quinone diazide sulfonyl acid halide and a multi ring polyhydroxyphenol to increase the size of the molecule and the number of moles of the light sensitive component substituted on the molecule.
Esters of naphthoquinone diazide sulfonyl halides and phenols are well known in the art and are described by DeForest, supra, pages 47-55, incorporated herein by reference. Such photoactive compounds and the methods used to make the same, are all well documented in prior patents including German Pat. No. 865,140 granted Feb. 2, 1953 and U.S. Pat. Nos. 2,767,092; 3,046,110; 3,046,112; 3,046,119; 3,046,121; 3,046,122; and 3,106,465, all incorporated herein by reference. Additional photoactive compounds that have been used in the formulation of positive-acting photoresists are shown in U.S. Pat No. 3,637,384, also incorporated herein by reference. These materials are formed by reaction of a suitable diazide of an aromatic sulfonyl chloride with an appropriate resin amine. Methods for the manufacture of these photoactive compounds and examples of the same are shown in U.S. Pat. No. 2,797,213, incorporated herein by reference. Other positive-working diazo compounds have been used for specific purposes. For example, a diazo compound used as a positive-working photoresist for deep UV lithography is Meldrum's diazo and its analogs as described by Clecak et al, Technical Disclosure Bulletin, Volume 24, Number 4, September 1981, IBM Corporation, pp. 1907 and 1908. An o-quinone diazide compound suitable for laser imaging is shown in U.S. Pat. No. 4,207,107. The aforesaid references are also incorporated herein by reference.
The resin binders most frequently used with the o-quinone diazide photoactive compounds in commercial practice are the alkali soluble phenol formaldehyde resins known as the novolak resins. Photoresists using such polymers are illustrated in U.K. Pat. No. 1,110,017, incorporated herein by reference. These materials are the product of reaction of a phenol with formaldehyde under conditions whereby a thermoplastic polymer is formed with a glass transition temperature of about 100.degree. C. Novolaks with glass transition temperatures in excess of 100.degree. C. are also known and exemplified in U.S. Pat. No. 5,266,440, which discloses novolak resins comprising the product resulting from the acid condensation of an aromatic aldehyde with a phenol resulting in resins having a molecular weight in excess of 1,500 Daltons and glass transition temperatures in excess of 125.degree. C.
Another class of binders used with such photoresists are homopolymers and copolymers of vinyl phenol. Photoresists of this nature are disclosed in U.S. Pat. No. 3,869,292, supra.
In the prior art, the above-described positive resists using alkali soluble phenolic resins as a binder are most often used as masks to protect substrates from chemical etching in photo-engraving processes. For example, in a conventional process for the manufacture of a printed circuit board, a copper-clad substrate is coated with a layer of a positive-working photoresist, exposed to actinic radiation to form a latent circuit image in the photoresist coating, developed with a liquid developer to form a relief image and etched with a chemical etchant whereby unwanted copper is removed and copper protected by the photoresist mask is left behind in a circuit pattern. For the manufacture of printed circuit boards, the photoresist must possess chemical resistance, must adhere to the circuit board substrate, and must be capable of fine-line image resolution.
Similar photoresists are also used in the fabrication of semiconductors. As in the manufacture of printed circuits, the photoresist is coated onto the surface of a semiconductor wafer and then imaged and developed. Following development, the wafer is typically etched with an etchant whereby the portions of the wafer bared by development of the photoresist are dissolved while the portions of the wafer coated with photoresist are protected, thereby defining a circuit pattern. For use in the manufacture of a semiconductor, the photoresist must possess resistance to chemical etchants, must adhere to the surface of the semiconductor wafer and must be capable of very fine-line image resolution.
Positive working photoresists are more expensive than negative working photoresists due primarily to the cost of the PAC. This component is costly and used in significant concentration. Though it is disclosed in the literature that o-quinone diazide PACs may be used in amounts of only several percent of the total solids content of the photoresist, in commercial practice, it has been found that the PAC is required in amounts of at least about fifteen percent by weight to provide a photoresist coating capable of providing a high resolution image. For this reason, it is recognized in the art that it would be desirable to find a means to maintain the resolution capability of a photoresist coating while reducing the concentration of the naphthoquinone diazide sulfonic acid ester PAC component or to improve the resolution capability of such a coating without concomitant increase in the concentration of the PAC.
In U.S. patent application Ser. No. 08/510,709 filed Aug. 3, 1995, assigned to the same assignee as the subject application and incorporated herein by reference, a photoresist composition is disclosed comprising an alkali soluble resin binder, a naphthoquinone diazide sulfonic acid ester PAC and a vinyl ether compound. The photoresist is one characterized by a reduced